Dr. Dustin Ballard: Don't blame it on the shots

DID YOU KNOW that the more ice cream you eat, the thinner you are? It's surprising, but true. If you track the average person's weight over the course of a year, you'll find he or she's lighter when more ice cream is consumed and heavier when less is eaten.

But wait. Before you stock up on pints of Cold Stone Creamery and shares of Three Twins, I should mention that people eat more ice cream in the summertime. They are also more active and have higher metabolic rates in warmer weather. So, perhaps it's not the ice cream that leads to weight loss, but rather seasonal variation in calorie burning. What's the lesson here? That causality can be elusive.

Causality simply means "cause and effect." Determining whether there is genuine causality between two entities, rather than a chance association or one unduly influenced by unrecognized factors, is difficult. For example, many people still believe that exposure to cold weather causes pneumonia. But, it's not actually the chilled air that increases the risk of pneumonia, it's that during colder weather folks are more likely to stay inside in closer proximity to other people's germs.

Proving a clear-cut link between a dietary item, personal habit or medical treatment and a disease process is fraught with the potential for misinterpretation. Consider the just-won't—go-away proposed connection between routine childhood vaccinations and autism.

The diagnosis of childhood autism is on the rise and we are not sure why. Since the 1990s, autism rates have increased dramatically. As a parent, I have experienced a good deal of anxiety about this. I have a niece and nephew who have each been diagnosed with an autism spectrum disorder (ASD), and my wife has repeatedly agonized about the immunization process for our own children. But as a medical professional, I have unabashedly preached that routine immunization programs are critically important for the public's health. After all, vaccination efforts have a proven track record: they eradicated smallpox and made polio a disease only seen in paranoid communities. Nonetheless, the belief that routine shots could permanently alter the neurochemistry of children is frightening.

Fortunately, there exists an overwhelming preponderance of medical research against the "vaccines-cause-autism hypothesis." Vaccination efforts during the past century have made certain childhood diseases so rare that they seem like remnants of an uncivilized past. Few of us have actually seen a new case of polio or measles, so it's easy to be lulled into thinking that they couldn't possibly cause trouble again. In contrast, the primary scientific evidence supporting a link between vaccines and autism was a small study published in the medical journal Lancet in 1998 — a study that has been thoroughly discredited. Since its publication, it has come to light that there was a conflict of interest (the research was secretly funded by plaintiff lawyers) and that the data was falsified. Its findings (linking intestinal inflammation with the MMR immunization and subsequent autism) have not been replicated in larger studies and have been repudiated by the coauthors and retracted by the journal.

This is not a new story or topic. But, I dredge it back up since parental concern about the safety of vaccines persists. This is especially true in Marin, and our county continues to put itself at risk through clusters of unvaccinated children.

Take the data on personal belief exemptions (PBEs) for school-mandated vaccinations. In 2013, once again Marin led the way in the Bay Area with a PBE rate of 7.8 percent. Of particular concern is the disparity in PBE rates at different schools. Because of herd immunity (immunity that occurs when the vaccinated part of the community — or herd — provides protection to unvaccinated individuals) many parents think that their children are protected against childhood diseases even if they are not fully vaccinated. That may be true, or may not, and in this regard it matters how many other children in the surrounding area and school are vaccinated. Thus, children at the New Village School in Sausalito, home to a 74 percent PBE rate, are certainly at higher risk of vaccine-preventable diseases (like a potentially life-threatening one like whooping cough) than those at my daughter's school (Hidden Valley, 7 percent PBE). You can look up the PBE rate at your child's school at: http://bit.ly/1gViuMk.

Those of us in the medical community hope that state law AB 2109, which passed this year and takes effect Jan. 1, will help improve such differences. Rather than just signing a form for a PBE exemption, the law requires parents to meet with a health-care provider to discuss the risks and benefits of vaccines before a PBE will be granted. The intent is not to block PBEs (there are many possible reasons why parents might file one), but to provide accurate information and deter exemptions filed purely out of convenience.

You can expect to hear more about this new law as we move forward into 2014. Dr. Matt Willis, Marin County Public Health Officer, says "This is an invitation for new dialogue about vaccination between parents and trusted providers, and for the community as a whole. By grounding these conversations in real evidence, and listening to any fears and concerns, we can help vaccine-hesitant parents make a more informed choice."

Thus, we hope that AB2109 will help up clear up some of the misinformation about vaccines and encourage parents to make informed decisions. No medical treatment is completely risk-free, but routine childhood immunizations are clear winners in any cost-benefit analysis.

Despite its indisputable deliciousness, the same cannot be said of ice cream.

Dr. Dustin W. Ballard is an emergency physician at Kaiser Permanente San Rafael and the author of "The Bullet's Yaw: Reflections on Violence, Healing and an Unforgettable Stranger." His Medically Clear column appears every third Monday; follow him on Twitter at http://twitter.com/dballard30.